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# How do I increase DC voltage?

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#### ME-209

##### Newbie level 3
Hi everyone - new to this board - thank you in advance for the help....

Here is my challenge:

I am trying to increase voltage on a DC circuit from 3V (2 AAA batteries) to 80V as efficiently as possible. The current draw will be somewhere in the vicinity of 160 mA, and the signal consists of alternating polarity impulses with a very small duty cycle. In addition to a reasonable efficiency, heat dissipation and component costs are of concern (i.e., the solution needs to be suitable for mass production).

My background is mechanical engineering, so using a 10x DC-to-DC transformer seems like a plausible solution.

Questions

1) Will me above simple solution work?
2) If not, why? And what can I do instead?

Thank you and happy circuitry,
Kermit

3V AAA's can supply 100mA for a short period before dying well under an hour or so.
V*I= 0.3 watts is a practical limit. continuous.

You require 80V * 0.16A = 12.8W * duty cycle therefore the duty cycle must be 0.3W/12.8= ~2% or much much smaller.

A project purpose would also be valuable
with other specifications such as discharge power ( 1/2CV^2) or VI*T x f where T is the 50% pulse width and f the repetition rate and battery life.

Your battery is probably under powered.

You may need to use a LiPo battery and define the output power * Duty cycle and battery life in order to size this design.

Can you define these?

I will go one step further:
with such low primary voltage, your efficiency will be no higher than 60% with low cost circuitry, and I'm being generous.
That means that the batteries require to supply 21 Watt power pulses, or about 7 amps.

Sincerely, I can't see a pair of AAAs and its associated battery holder capable of supplying that, even at low duty cycle.

Have to agree with all of the above.
Its a big ask for any AAA battery.

Only way I can see something like this working may be with a boost converter at very low power, and store the energy in a capacitor at 80v (or more).
Something that gates on and off to hold the capacitor up at 80v.

If the duty cycle is truly very low, like 1% and the pulses very short, with a long recharge interval in between it might work.
But battery life is still likely to be unacceptably short for most practical applications.

Obviously, an exact specification of the "very small duty cycle", pulse and idle time is essential for a real design.

A new fully charged Energizer AAA Ni-MH cell has an internal resistance of 35 milli-ohms. Then its voltage drop is only 0.2V with a load current of 5.7A.
But since it is small its capacity is low and its internal resistance quickly rises causing its voltage drop to increase.

The fairly small Li-Po batteries for my radio controlled model airplanes can provide MANY Amps, enough to vaporize their wires. You can select their size which determines their capacity.

Thank you for the response. First, just to clarify, the plan is to use two alkaline 1.5V AAA batteries in series rather than a 3V AAA battery. The duty cycle will be low - pulses of a 250 microsecond duration and frequency of 25 Hz. That should be well under 1%.

The duty cycle will be low - pulses of a 250 microsecond duration and frequency of 25 Hz. That should be well under 1%.

If you will use Name Brand AAA alkaline cells then you should look at the datasheet to see that their voltage drop is high when the current is only one amp and their voltage runs down a lot as they are used.

O/k so duty cycle is 250uS every 40mS or 1/160

And our load current is 160ma, which is 1mA averaged over the whole period.
Total averaged power 80mW.

So what I think you need to do is step up the 3v to 80v with a low power boost converter into a storage capacitor. Then pulse the voltage through the load for 250uS using up only a small proportion of the total stored charge on the capacitor.

A wild guess might be something like 50% efficiency or 160mW constant battery load. That is about 53mA

The closest discharge figures I can find here for an AAA alkaline suggest 20 hours at 40mA down to 0.9v

I have absolutely no idea what the final efficiency might end up at, but perhaps 15 to 24 hours total running time might be within the realms of possibility.

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